Nutrient Requirements of Dairy Cattle: Changes Made in the 2021 NRC

Approximately every 15 years, the National Academy of Sciences appoints a committee of nutrition experts to evaluate current feeding standard for domestic livestock. The new Dairy Cattle Requirements publication was released in late 2021and will be the focus of this presentation. Changes from the 2001 NRC recommendations will be emphasized. Major changes include better equations to estimate dry matter intake, changes in energy supply and requirement calculations, and revisions for carbohydrate recommendations (fiber, starch, sugar, effective fiber, etc.). The protein supply and requirement system underwent a major change. Amino acids are now emphasized and responses to changes in amino acid and energy supply are used to estimate milk protein yield. Mineral and vitamin recommendations were evaluated and for most minerals and vitamins, recommendations underwent small changes. However, for magnesium, manganese, and copper, requirements or recommendations changed substantially. The tables of nutrient composition were extensively revised and probably are the best feed tables currently available. The book contains a completely revised young calf nutrient model. Ration evaluation software was produced along with the new book. The software includes all the changes discussed in the book and output now includes environmental impact. The new book and software represents current state of the art in feeding dairy cattle.